Circuit for operating electric discharge lamps



1951 V G. c. DUCKETT ET AL 7 2,570,780

CIRCUIT FOR OPERATING ELECTRIC DISCHARGE LAMPS Filed Aug. 5, 1948 INVENTORS (femyw CLIFFORD DUCKFTT 11 ND qua-wavy HYDN ouuay BY d q-r'l oRu eY Patented Oct. 9, 1951 CIRCUIT FOR OPERATING ELECTRIC DISCHARGE LAMPS Gerald Clifford Duckett, North Harrow, and Anthony Haydn Willo'ughby, Garston, Watford, England, assignors' to General Electric Company, Limited, London, England Application August 5, 1948, Serial No. 42,556

In Great Britain August 11, 1947 I This invention relates to electric circuits for operating gas or vapour filled electric discharge lamps from a D. C. supply, of the type comprising an electromagnetically operated switch adapted in operation of the circuit to short-circuit the discharge lamp when closed and when thereafter opened to give rise to a high-voltage pulse in virtins of inductance present in the circuit which pulse is applied across the lamp and causes-the discharge to start.

The lamps for use with such circuits are usually designed to have a specially activated electron emissive cathode and an anode, and it is important, to avoid damaging the lamp, that the highvoltage starting pulse should never be applied withthe lamp connected to the supply in the reverse direction, i. e. anode to the negative and cathode to the positive pole of the supply, for then. a discharge might start in the reverse direction and damage the cathode.

It is not likely that the lamp will be connected in the wrong direction to the lamp-terminals of the circuit since the lamp and lamp-terminals are or may be designed to prevent reverse connection of the lamp; wrong connection of the lamp is more likely to arise from wrong connection of the supply-terminals of the circuit to the D. C. supply.

The object of the invention is to reduce the possibility of damage to the lamp arising from wrong connection of the supply-terminals to the D. C. supply.

According to the invention in an electric circuit of the type specified the operating coil of the electro-magnetic switch is connected for supply to the supply-terminals for the lamp circuit and an asymmetric rectifier is included either in series or in shunt with the said operating coil, the sense of the rectifier and its resistance for each direction of applied voltage being such that the current flowing through the said operating coil is insufficient to operate the switch when the lamp and coil are connected to the D. C. supply in the reverse polarity but is sufiicient to operate the switch when the lamp and coil are connected to the D. C. supply in the correct polarity.

The term asymmetric implies that the effective resistance of the rectifier must be greater for one polarity of voltage applied across it than for the other polarity. A single metal rectifier is thus asymmetric but a bridge circuit of four rectifiers arranged as a full wave rectifier is symmetrical and not suitable for use in accordance with this invention.

Preferably the rectifier is connected in shunt 4 Claims. (Cl. 315-103) with the coil, the sense of the rectifier then being such that it is of the higher resistance when the lamp and coil are connected to the D. C.

supply in the correct polarity; usually it will then be necessary or desirable to include acurrntlimiting resistance in series with the rectifiercoil combination, for limiting the rectifier current on connection in the reverse polarity, and this may conveniently be provided by an indicator lamp which is arranged to give no indication when the lower voltage is dropped across it, i. e. when'the discharge lamp is connected to the D. C. supply in the correct polarity, but to light up when the higher voltage is dropped across it, i. e. when the, discharge lamp is connected to the D. C. supply in the reverse polarity.- One circuit arrangement in accordance with theinvention, which will now-be described by way of example, is shown diagrammatically in the accompanying drawing;

Referring to the drawing, a lamp 1 which may be 'for example, a'2,500 watt high pressuremercury vapour lamp of the compact source type, is adapted to be connected in pre-arranged polarity through lamp-terminals 2, 3, here shown as associated respectively with the anode and cathode of the lamp, by leads 2', 3' to a D. C. supply, the leads 2, 3' being connected respectively to the positive supply-terminal l3 and the negative supply-terminal M, the supply-terminals being adapted to be connected to the D. C. supply in the polarity indicated. Between the positive supply-terminal l3 and the positive lamp-terminal 2 there are connected in series an inductance coil 4 of low self-capacity and a resistive stabilising impedance 5; between the negative supply-terminal I4 and the negative lamp-terminal 3 is connected the operating coil 8 of a relay whose function is described below.

The electro-magnetic switch 6 is a vacuum switch and is connected across the lamp terminals, being connected to lead 2 at a point between the inductance coil 4 and the positive lampterminal 2, and being connected to lead 3 at a point between the relay coil 8 and the negative supply-terminal I47; the operating coil 1 of the vacuum switch is connected across the supplyterminals in series with an operating switch I 0, an indicator lamp I I of the incandescent filament type which acts also as a current-limiting resistor, and the contacts 9 of the said relay.

The latter, with its contacts, is included in the circuit as described in Patent No. 2,557,809, dated June 19, 1951, which matured from copending United States patent application, Serial No.

3 42,555, filed August 5, 1948, by Anthony Haydn Willoughby for Circuits for Operating Electric Discharge Lamps and assigned to the assignee of the present application. Said relay ensures that once theavacuumaswitch 6 has been operated to start the discharge lamp; I, the operating coil T of the vacuum switch is opened-circuited, by

opening of the relay contacts 9 actuated by the lamp current flowing through the relay-operating coil 8, for so long as the lamp current i'sefi'o'w ing, so that the discharge lamp cannot' be ex;-

itinguished by accidental operation of the said,

operating switch l0; this relay arrangement is not an essential part of the. cii'cuit-in accordancewith the invention, but has been included to-in =dicate how it may be incorporated in the circuit in accordance with the invention;

Across the operating coil I of the vacuum switch is shunted a rectifier l2 of the plate type which is directed to be the higher impedance. forthecorrect. polarity of connectioniotthe supply-terminals. to the D'. Crsupply, andl isof suchlower impedance in the: reverse direction that the operating coil 1 islinsufiiciently energisedto operate the vacuum switch 6 if'the supply-terminals are connected to the D1 C. supply- ,inethe reverse polarity; the indicator lamp l'l is' arrangedso as then to light up-to indicate the incorrect connection.

We claim:

1. An electric circuit for operating from adirect current supply an electric discharge lamp having a gaseous filling and an anode and oath:- ode requiring connection. to the" direct current supply in the correct polarity; which circuit comprises an inductance and a stabilizingresistance in-serieslwith the lamp, an electromagnetically operated starting switch including a pair of.n0r mally. open contacts and. an operating coil, a branch circuit including saidnormally open contacts and a branch circuit includinggsaid operating coil, both said branchlcircuits being in shunt with the lamp, the branch circuit which" includes the operating'coil having a pair of.normally open manually operable control contacts connected in series therein, the' branch circuit including the switch contacts and the branch circuit including the operating coil of the switch being connected on opposite sides of said inductance, with the first named branch closer to the lamp, whereby when the control contacts are closed by an op erator for starting the: lamp the operating coil will be energized" to close the contacts of the starting switch thus short-circuiting the lamp, and when the control contacts thereafter are opened the operating coil will be de-energized causing'the starting switch to open and thus produce a high voltage lamp starting pulse across said'linductance, and an asymmetric rectifier connectedzin thebranch circuit including the operating coil of the switch and directed for obtaining maximum current through the operating coil when the lamp anode is correctly connected to thepositiveterminal of the D. C. supply, the minimum current flowing on incorrect connection of the lamp anode to the negative terminal of the supply being insufficient to operate the switch.

2. A circuit'a'ccordingto claim 1 wherein-the rectifier is connected in shunt with the-operating" coilLo'f the electromagnetic switch and di" rected so that the rectifier has its maximum resistance when the'lamp anode is connected to the positive terminal of the D. C. supply.

3..A circuit according to claim 2 wherein a; current-limiting resistance is connected in series with the rectifier-operating coil combination:

4. A circuit according to claim 3 wherein the said current-limiting resistance is provided by an indicator lamp which is adapted to light up when the anode is connected to the negative terminal of the D. C. sup-ply.

GERALD CLIFFORD DUCKETTQ ANTHONY HAYDN WILLO-UGHBYI REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES- PATENTS Number Name Date 2,18l,294 Biggs Nov. 28, 1939 2 ,27 2j770" Edwards Feb; 10,.194'2' 

